Ball and socket joints are known structures which are commonly used between load transmitting members which must move relative to each other. Typically, ball and socket joints include a ball-ended stud for connection with one of the relatively movable members and a socket which is connected with the other of the relatively movable members. The ball stud includes a ball portion which is located in a chamber defined by the socket. A bearing arrangement is provided between the ball portion of the ball stud and the socket to transmit forces between the ball stud and the socket and to permit relative movement between the ball stud and the socket.
One type of such bearing arrangement comprises bearing elements located in the socket and which have bearing surfaces on which the ball portion of the ball stud slides. Such constructions are susceptible to moisture, dirt, salt and other forms of contamination, reducing the life of the ball joint. Boot seals packed with grease are frequently used with such joints in order to provide for protection of the bearing surfaces.
Another type of bearing arrangement which is known is shown in U.S. Pat. Nos. 2,979,353; 3,843,272; and 4,235,558. These patents disclose ball joints having an elastomeric bearing material located between the ball portion of the ball stud and the socket. In these structures, the elastomeric material is bonded to the ball portion of the ball stud. The elastomeric material is interposed between the ball stud and the socket and resiliently interconnects the ball stud and the socket. The elastomeric material deforms resiliently during relative movement between the ball stud and socket. Because of the resilient deformation of the elastomeric material, it urges the ball stud and socket back to an original relative position after the ball stud and socket are moved by forces relatively from such original relative positions.
The ball joints which use an elastomeric material between the ball stud and socket are subject to certain problems. One problem is that the elastomeric material may slip in the socket upon relative rotation of the ball stud and the socket. This slippage, if it occurs, results in the ball stud and socket not returning to the original relative position. One technique for minimizing the possibility of slippage of the elastomeric material has been to bond the elastomeric material to the socket. Such technique is disclosed in U.S. Pat. No. 3,843,272. The bonding process, however, is relatively expensive. Another technique has been to substantially compress or preload the elastomeric material between the ball and the socket. This causes the elastomeric material to be wedged tightly against the surfaces of the socket. This technique has resulted in a problem that may be referred to as "excess torque hysteresis". Specifically, the deformation creates significant compressive stresses internally of the elastomeric bearing. When such a ball stud and socket are relatively pivoted, a portion of the elastomeric material which is deformed during assembly will be moved in opposition to the compressive stresses and, depending on the amount of movement between the ball stud and socket, may be placed in tension. When the forces causing the relative movement of the ball stud and socket are removed, the elastomeric material will not, because of the initial internal compressive stress, return to its original position, and therefore, the ball stud and socket will not be returned to their original relative positions.
Also, ball joints using elastomeric bearing material typically have the elastomeric material almost totally surrounding the ball portion of the ball stud. For example, this construction is shown in U.S. Pat. No. 4,235,558. When the elastomeric material totally surrounds the ball portion of the ball stud, relative pivoting movement between the ball stud and the socket results in a large volume of elastomeric material being distorted or deformed. As a result, there is a relatively high effort required to effect relative pivotal movement of the ball stud and socket as compared to a joint using the same elastomeric material not totally surrounding the ball portion.